This invention relates to a pin driven into a sweeper made of a synthetic resin for scraping scale from the inner wall of a pipe.
Scale or slag can deposit on the inner wall of a pipe for supplying water, petroleum or various types of gases and can eventually reduce the effective cross sectional area of the pipe and thus impede the flow of fluids therethrough. For this reason, the inner wall surface of the pipe is cleaned periodically to remove the scale.
To clean a pipe of the type described, a sweeper (also referred to as a "pig") made of synthetic resin and having a conical portion at its forward end is inserted into the pipe while being elastically deformed, hydraulic pressure is applied to the rearward end of the sweeper within the pipe, and the scale on the inner wall of the pipe is scraped off by the sweeper while the sweeper is advanced through the pipe by a difference in pressure between the forward and rearward end of the sweeper. The scraping off of the scale is actually performed by the heads of a number of metal pins driven in toward the center of the sweeper from the outer peripheral surface thereof. The heads of these pins advance together with the sweeper while being brought into pressured contact with the inner wall of the pipe and strike the scale to remove the same from the inner wall. The pins are made of a material not as hard as that of the pipe and somewhat harder than that of the scale or slag to be scraped off from the inner wall of the pipe.
Pins of this type and a sweeper equipped with the pins have already been proposed by the inventor in Japanese Patent Publication (KOKOKU) No. 58-36634 and Japanese Utility Model Publication (KOKOKU) No 58-45831.
The heads of these pins have a generally square shape or a round configuration the outer surface of which is formed to include grooves of a grid-like pattern. Since it is impossible to replace these pins after they are driven into the sweeper, the sweeper reaches the end of its service life when the pin heads are worn too much to scrape off the scale. In the case of the square head, for example, the corner portions become rounded due to wear. With the head having the round configuration, wear can cause the grooves to vanish completely. In either case, the sweeper will loose its ability to scrape off scale, so that a new sweeper must be used in place of the old.
Since the ability of the pins to scrape off scale is directly linked to the service life of the sweeper, the shape of the pins is a very important factor in determining the life of the sweeper.